Metal-flake manufacturing apparatus

ABSTRACT

Cooling rolls are spaced to have a gas of a size greater than thickness of metal thin bodies to be produced. A nozzle is arranged to eject molten metal onto a surface of the cooling roll. The first cooling roll quenches molten metal ejected from the nozzle into metal thin bodies. On the next cooling roll, the produced metal thin bodies are hit into flakes and excessive molten metal is made into metal thin bodies. Thus, freedom of supplying the molten metal flakes can be efficiently produced.

TECHNICAL FIELD

The present invention relates to a metal-flake, manufacturing apparatuswhich can simply and efficiently manufacture quenched metal-flakematerials required for manufacture of thermoelectric materials, magnetmaterials, hydrogen absorbing alloys or the like.

BACKGROUND ART

Thermoelectric materials, magnet materials, hydrogen absorbing alloys orthe like, which may be often intermetallic compounds, may be produced bycrushing ingots. Conceived as an alternative way aimed at effectiveimprovement of performances is to use quenched metal-flake materials,which way utilizes, as quench effects, compositional uniformity andcrystal orientation along a quenching direction.

Such metal flakes are produced by preliminarily producing a continuous,wide-width thin strip and then crushing or shearing this continuous thinstrip. Mainly used to produce such continuous thin strip is a single ordouble roll method.

In the single roll method, as illustrated in FIG. 1A, molten metal isejected from a nozzle 2 arranged above a cooling roll 1 to stably keep amolten metal reservoir (puddle), using surface tension of the moltenmetal, on a top of the cooling roll 1 which contacts the molten metal,thereby producing a continuous, wide-width thin strip which is receivedin a storage box 3.

In the double roll method, as shown in FIG. 1B, just above a nip betweentwo cooling rolls 4 which are arranged to contact with each other,molten metal is fed through a nozzle 5 and is solidified and rolled downbetween the cooling rolls 4, thereby producing a continuous thin stripwhich has been cooled at its opposite surfaces.

The single roll method, however, has a problem that the molten metalreservoir (puddle) is difficult to stably keep at the top of the coolingroll 1. If the molten metal is excessively ejected, the molten metalreservoir may become unstable and drop sideways or backward of thecooling roll 1 or get mixed with the thin strip product to thereby lowerthe uniformity of the finished product.

In the double roll method, on the other hand, the cooling rolls 4 areused not only for cooling and solidification operations but also forrolling-down operation so that a large drive power is required for thecooling rolls 4 and the cooling rolls 4 tend to be severely damaged.

Moreover, obtained as a product in either of the conventional methods isa continuous thin strip which is low in bulk density. Therefore, alarge-sized storage box is required; alternatively, a separate crusheror shearing machine is required upstream of a storage box.

SUMMARY OF THE INVENTION

The present invention was made in view of the above problems of theprior art and has its object to provide a metal-flake manufacturingapparatus which can overcome the problem on stable supply of moltenmetal in the single roll method and the problem on roll-drive power inthe double roll method and which can manufacture quenched metal-flakematerials in a simple and highly efficient manner.

The inventors have reviewed quenched metal materials required formanufacture of thermoelectric materials, magnet materials, hydrogenabsorbing alloys or the like to find out that utilized as quench effectsin a thin strip are compositional uniformity and crystal orientationalong a quenching direction and that to provide a continuous thin stripis not always a requisite since the thin strip is sheared or crushed ina next step. The invention was completed on the basis of such findings.

More specifically, in order to overcome the above problems, a pluralityof cooling rolls are spaced to have a gap or gaps of a size greater thanthickness of metal thin bodies to be produced. A nozzle is provided toeject molten metal onto a surface of such cooling roll. The firstcooling roll quenches the molten metal from the nozzle into metal thinbodies. On the next cooling roll, the produced metal thin bodies are hitinto flakes while the excess molten metal is made into metal thinbodies. Thus, freedom in supply of molten metal is enhanced and metalflakes can be stably and efficiently produced.

The cooling rolls are arranged at different heights so that the producedmetal thin bodies are sequentially hit on the rolls, which increaseschances of the produced metal thin bodies being hit on the cooling rollsand contributes to obtaining further finer flakes and changeability ofthe flake withdrawal direction.

Rotational axes of the cooling rolls may be out of parallelism so that aflying direction of the metal thin bodies, which is on a planeperpendicular to the rotational axis, may be changed with increasedfreedom.

Moreover, the cooling rolls may be arranged to rotate at differentperipheral velocities. Differentiation in peripheral velocity betweenthe cooling rolls will contribute to controlling the thickness of themetal thin bodies produced; if the cooling rolls with the same diameterwere driven to rotate at the same peripheral velocity, thinner andthicker metal flakes would be produced on the upstream and downstreamrolls, respectively.

In addition, the cooling rolls may have different diameters so as tohave different peripheral velocities, which will contribute, just likethe above, to controlling the thickness of the metal thin bodies.

The nozzle may have a plurality of nozzle openings along the axis of thecooling roll. Provision of the nozzle openings in the shape of, forexample, slot or a circle, along the axis of the roll will contribute tofurther effective production of metal flakes.

The nozzle opening may have a sectional area of 0.7878-78 mm². Even withthe nozzle openings having the sectional area as large as of 28-78 mm²,which are unusually large as compared with those in the conventionalproduction of metal flakes, thick metal flakes can be produced withhigher efficiency. The shape of the nozzle openings are not limited tocircle.

The nozzle and the cooling rolls may be placed in atmospheric gas andwindbreak members may be arranged to prevent the atmospheric gas frombeing swirled by the rotating cooling rolls. Manufacturing in theatmosphere such as inert gas will enhance the quality of the metalflakes produced. Prevention of the atmospheric gas from being swirled bythe rotating cooling rolls will prevent the nozzle-from being cooled andprevent the metal flakes from being scattered.

Furthermore, gas from atmospheric gas supply nozzles may be directed toguide the metal flakes towards a storage box in which metal flakes areto be stored, which will prevent the metal flakes from being scatteredand contribute to efficient collection of the metal flakes in the box.

The storage box may have a cooler for cooling the collected metalflakes, which will contribute to further improvement of the metal flakecooling efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are illustrations of single and double roll methods,respectively, with respect to conventional metal thin stripmanufacturing apparatuses;

FIG. 2 is a schematic diagram of an embodiment of the metal-flakemanufacturing apparatus according to the invention with two coolingrolls;

FIGS. 3A-3B and 3C show numbers and arrangements of the cooling rolls infurther embodiments of the metal-flake manufacturing apparatus accordingto the invention;

FIGS. 4A and 4B are schematic perspective and plan views, respectively,of an embodiment of the metal-flake manufacturing apparatus according tothe invention;

FIG. 5 is a schematic diagram of an embodiment of the metal-flakemanufacturing apparatus according to the invention where two coolingrolls with the same diameter are used:

FIG. 6 is a schematic diagram of an embodiment of the metal-flakemanufacturing apparatus according to the invention where two coolingrolls with different diameters are used;

FIG. 7 is a graph showing the relationship between rotational frequencyof rolls and average thickness of metal flakes in an embodiment of themetal-flake manufacturing apparatus according to the invention using twocooling rolls with the same diameter;

FIGS. 8A and 8B are sectional views of a nozzle portion of furtherembodiments of the metal-flake manufacturing apparatus according to theinvention; and

FIG. 9 is a graph showing the relationship between nozzle diameter andflake thickness in a still further embodiment of the metal-flakemanufacturing apparatus according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described with reference to thedrawings.

FIG. 2 is a schematic diagram of an embodiment of the metal-flakemanufacturing apparatus according to the invention with two coolingrolls.

This metal-flake manufacturing apparatus 10 comprises two, hollowcooling rolls 11 and 12 which are internally cooled. The two coolingrolls 11 and 12 are arranged at different heights such that the secondroll 12 downstream in the direction of supply of the molten metal has arotational axis which is upwardly offset to that of the upstream, firstcooling roll 11 and that the two cooling rolls 11 and 12 are spaced tohave a gap of a size greater than thickness of metal thin bodies to beproduced. The thickness of the produced metal thin bodies issubstantially dependent upon cooling capability and rotational frequencyof the cooling roll 11. If the thickness of the metal thin bodies is50-60 μm, then the gap between the cooling rolls 11 and 12 is to be ofthe order of 3 mm.

These cooling rolls 11 and 12 are driven to rotate in oppositedirections such that flakes are moved from above to below intermediatelybetween the cooling rolls 11 and 12. They are driven by a drive (notshown) to rotate, for example, at peripheral velocities of the order of10-50 m/sec.

Arranged above the first cooling roll 11 are a tundish 13 and a nozzle14. Molten metal fed to the tundish 13 is ejected via the nozzle 14 ontothe first cooling roll 11.

This nozzle 14 is arranged to eject the molten metal to a surface of thefirst cooling roll 11 at a point downstream of the top of the roll inthe direction of its rotation, whereby the molten metal, even ifexcessively ejected, may be splashed not backwards but forward of theroll. For example, the nozzle 14 may be disposed such that the moltenmetal is ejected to the surface of the first cooling roll 11 at a pointangularly downstream of the top of the roll in the direction of itsrotation by 45° or so in terms of center angle.

The nozzle 14 may have one or more nozzle openings. The multipleopenings may be arranged in parallel with the axis of the first coolingroll 11, which makes it possible to produce metal thin bodies inmultiple streams; alternatively, a metal thin body with a large widthmay be produced, though it is not a requisite at all.

The nozzle 14 is arranged with a distance from the surface of the firstcooling roll 11. This distance is set to be larger than that between theconventional single roll and nozzle since it is not necessary to producea wide and continuous strip.

This nozzle 14 used has opening or openings which may be in the shape ofcircle or slot. In the case of the circular openings, their diameter ispreferably no more than 3 mm and its sectional area, no more than about7.1 mm² from the viewpoint of improving the yield of the produced metalflakes. However, those with the diameter of more than 3 mm and thesectional area of more than about 7.1 mm² are also allowable, in whichcase thicker metal flakes will result.

It should be noted that the nozzle opening shape is not limited tocircular, provided that the stated a sectional area is secured.

Furthermore, if the nozzle 14 is provided with a heater/heat retainer orthe like, the molten metal is prevented from-being solidified at thenozzle and thus a stable operation can be ensured.

Provided below such two cooling rolls 11 and 12 is a storage box 15 tocollect metal flakes which have been obtained by hitting the metal thinbodies, which has been solidified on the first cooling roll 11, onto thesecond cooling roll 12 into flakes as well as by cooling and solidifyingthe molten metal, which are not cooled and solidified on the firstcooling roll 11 but are splashed, on the second cooling roll 12.

For efficient withdrawal of the metal thin bodies to the storage box 15,a guide tube 16 is arranged between beneath the two cooling rolls 11 and12 and the storage box 15, so that the metal flakes are collected in thestorage box 15 without being scattered.

This metal-flake manufacturing apparatus 10 is entirely enclosed in asealed container 17, allowing the metal flakes to be produced in anatmospheric gas such as an inert gas. The sealed container 17 ispartitioned into upper and lower sections by a preload wall 18 at abottom of the tundish 13.

Atmospheric gas supply nozzles 19 are disposed in the sealed container17 below the rolls 11 and 12 such that the gas is ejected respectivelyfrom the nozzles to the flow of flakes produced by the rolls 11 and 12,whereby the produced metal flakes are cooled and can be guided to thestorage box 15 using the flow of the inert gas.

The injected inert gas is sucked by a blower (not shown) via a gassuction inlet on the storage box 15, is cooled by a heat exchanger 20and then re-supplied via the atmospheric gas supply nozzles 19 forcirculation.

In this metal-flake manufacturing apparatus 10, whirls are generated bythe cooling rolls 11 and 12 as the atmospheric gas such as inert gas isswirled due to high-velocity rotation of the cooling rolls in theatmospheric gas. In order to prevent the nozzle 14 from being cooled bythe whirls and in order to prevent the metal thin bodies from beingscattered by the whirls, windbreak plates 21 are protruded from thepreload walls 18 at the sides of the nozzle 14 toward the cooling rolls11 and 12.

Furthermore, in order to keep the surfaces of the cooling rolls 11 and12 clean, a cleaning brush 22 in the form of roll is provided for eachof the cooling rolls 11 and 12 in such a manner as to contact an outerperiphery of each roll.

Mode of operation of the metal-flake manufacturing apparatus 10 thusconstructed and manufacturing of metal flakes will be described.

With the metal-flake manufacturing apparatus 10 being supplied with theinert gas from the atmospheric gas supply nozzles 19, metal molten in asmelter is fed to the tundish 13 and is ejected onto the first coolingroll 11 which is driven to rotate and is internally cooled.

The molten metal, as it contacts the surface of the first cooling roll11, is substantially solidified into a thin strip which is hit on asurface of and is crushed by the second cooling roll 12. The moltenmetal which was not solidified on the first cooling roll 11 but splashedforward into smaller chunks is hit on a roll surface of and is cooledand solidified by the second cooling roll 12, whereby the respectivechunks of the molten metal are turned into flakes.

The metal thin bodies in the form of metal flakes thus obtained by thefirst and second cooling rolls 11 and 12 are further hit on the surfaceof and are further crushed into flakes by the first cooling roll 11, andare guided and withdrawn into the storage box 15 by the guide tube 16 aswell as by the flow of the inert gas fed from the atmospheric gas supplynozzles 19.

Thus, the metal thin bodies produced through the respective steps areefficiently cooled by the atmospheric gas during their travels from thefirst cooling roll 11 to the second cooling roll 12, from the secondcooling roll 12 back to the first cooling roll 11 and finally to thestorage box 15 via the guide tube 16. Also in the storage box 15, theyare cooled by the circulated inert gas. Thus, the metal flakes areefficiently cooled.

According to such metal-flake manufacturing apparatus 10, unlike thecase of the single roll method, there is no need to adjust the amount ofmolten metal fed to the cooling roll for the purpose of forming a stablepuddle between the nozzle and roll, which contributes to simplifiedoperation; excess molten metal not solidified by the first cooling roll11, if any, can be cooled by the second cooling roll 12 and withdrawn inthe form of metal flakes, thereby substantially increasing the yield.

The metal flakes collected in the storage box 15, which are results notonly of crushing by the second cooling roll but also of solidificationfrom small chunks of molten metal, have bulk density increased incomparison with the conventionally stored thin strips and can becollected in stacked manner in the small-sized storage box 15.

Though in the form of flakes, they can be collected to the storage box15 without being scattered since, according to this metal-flakemanufacturing apparatus 10, the resultant metal flakes due tore-collision against the first cooling roll 11 are guided and withdrawninto the storage box 15 by the guide tube 16 and the flow of the inertgas supplied from the atmospheric gas supply nozzles 19.

Furthermore, according to this metal-flake manufacturing apparatus 10,the cooling rolls 11 and 12 are arranged not in contact with each otherand there is no need to roll down the solidified metal between therolls. As a result, the cooling rolls 11 and 12 require less drive powerthan in the prior-art double roll method, which contributes tosubstantial decrease of damage on the rolls.

Moreover, according to this metal-flake manufacturing apparatus 10, theatmospheric gas can be supplied for production of metal flakes in anatmosphere of inert gas, which contributes to production of metal flakesof high quality. Whirls caused by the swirling of the atmospheric gas,if any, can be blocked by the windbreak plates 21, thereby preventingcooling of the nozzle 14 and scattering of the metal flakes.

A crusher may be provided before the storage box 15 in this metal-flakemanufacturing apparatus 10 for further crushing of the flakes.

In addition to the atmospheric gas supply nozzles 19, a cooler may beprovided in or around the sealed container 17 so as to cool the metalflakes.

Further embodiments of the metal-flake manufacturing apparatus accordingto the invention will be described with reference to FIGS. 3A to 3C.Explanation on parts or elements similar to those in the above-describedembodiment is omitted.

The metal-flake manufacturing apparatus 10 according to the inventionhas a plurality of cooling rolls the number and arrangement of which maybe various; for example, as shown in FIG. 3A, two cooling rolls 11 and12 may be used and arranged such that the metal thin bodies are firsthit on the first cooling roll 11 and then on the second cooling roll 12for withdrawal. Alternatively, as shown in FIG. 3B, the two rolls may bearranged such that the metal thin bodies are hit again on the firstcooling roll 11 after its collision with the second cooling roll 12before being withdrawn, thereby enhancing the crushing effects. Furtheralternatively, as shown in FIG. 3C, a third cooling roll 23 may beprovided for further crushing of the metal flakes from the secondcooling roll 12 as well as for change of the withdrawal direction intohorizontal direction so as to suppress the overall height of theapparatus.

Except for the number and arrangement of the cooling rolls, thestructural particulars of those alternative embodiments are the same asthat of the embodiment initially described above.

Those metal-flake manufacturing apparatus 10 in which the number andarrangement of the cooling rolls are varied can also produce the metalflakes in a similar manner.

Thus, the metal-flake manufacturing apparatus according to the inventioncan stably produce the metal flakes even if the molten metal is ejectedin larger quantity.

Since the thin strip can be crushed halfway during the process ofmanufacture, no separate crusher is required and the storage box can beof smaller size.

Moreover, the direction of collection of the metal flakes may be freelyvaried by varying the arrangement or number of the cooling rolls.

The damage to and the rotative drive power required for the coolingrolls can be reduced as compared with the conventional double rollmethod.

The metal flakes can be stably produced even if operational conditionssuch as shape of the nozzle may be varied in an extensive range, whichis suitable for mass-production of metal flakes of constant quality.

A still further embodiment of the metal-flake manufacturing apparatusaccording to the invention will be described with reference to theschematic perspective and plan views of FIGS. 4A and 4B. Explanation onparts or elements similar to those in the earlier embodiments isomitted.

A metal-flake manufacturing apparatus 30 according to the inventioncomprises a plurality of, for example two, cooling rolls 31 and 32 whichhave respectively rotational axes 31 a and 32 a not in parallel witheach other. Here, as illustrated, the second cooling roll 32 is disposedlower than and has its rotational axis 32 a skew to the rotational axis31 a of the first cooling roll 31, which arrangement is to alter thedirection of withdrawal of the metal flakes after being hit on the firstcooling roll 31 and then on the second cooling roll 32, so as to attainfor example compact in size of the apparatus.

The remaining structural particulars other than the rotational axes ofthe cooling rolls are the same as those in the earlier embodiments.

Such metal-flake manufacturing apparatus 30 with the rotational axes 31a and 32 a of the cooling rolls 31 and 32 being not in parallel witheach other can still produce the metal flakes in the same manner. Themolten metal ejected onto the first cooling roll 31 is solidified uponcontact with the surface of the first cooling roll 31 into a thin stripwhich flies along a plane 31 b perpendicular to the rotational axis 31 aand is hit on the surface of the second cooling roll 32. On this secondcooling roll 32, the metal thin strip having been solidified on thefirst cooling roll 31 is crushed into flakes while the splashed moltenmetal that failed to be solidified does contact the surface of thesecond cooling roll 32 to be cooled and solidified and turned intoflakes, flying along a plane 32 b perpendicular to the rotational axis32 a of the second cooling roll 32.

Accordingly, the flying direction of the metal flakes may be adjusted byvarying the arrangement of the rotational axes 31 a and 32 a of thecooling rolls 31 and 32, which enhances the degree of freedom inarranging the apparatus.

The positioning of the cooling rolls is not limited to that in the aboveembodiment but may be chosen as desired depending upon a required flyingdirection. Also, the number of the cooling rolls is not limited to twoand may be three or more so as to increase the degree of freedom inadjusting the flying direction.

Further embodiments of the metal-flake manufacturing apparatus accordingto the invention will be described with reference to FIGS. 5-7.Explanation on parts or elements similar to those already explainedabove is omitted.

FIGS. 5-7 show further embodiments of the metal-flake manufacturingapparatus according to the invention. FIG. 5 is a schematic diagram withthe two cooling rolls having the same diameter; FIG. 6 is a schematicdiagram with the two cooling rolls having different diameters; and FIG.7 shows a graph plotting the rotational velocity of the rolls againstthe average thickness of the metal flakes when the rolls have the samediameter.

In this metal-flake manufacturing apparatus 40 which has a plurality of,for example two, cooling rolls 41 and 42 adapted to have differentperipheral velocities, which is achieved by, for example,differentiating rotational velocities v1 and v2 of the first and secondcooling rolls 41 and 42 which have the same diameter as shown in FIG. 5;alternatively, the rolls may be driven to rotate at the same rotationalfrequency with, for example, the second cooling roll 43 being varied indiameter to have a varied peripheral velocity v3 as shown in FIG. 6.

Experiments were conducted to find the relationship between therotational velocities (peripheral velocities at outer peripheries) ofthe rolls and the average thickness of the cooled and solidified metalflakes. Experimental results are as shown in FIG. 7.

It is known that in accordance with the conventional single roll method,the thickness of the manufactured flakes decreases as the rotationalvelocity of the roll increases.

On the other hand, when two cooling rolls are used, the thickness of theflakes manufactured by the first cooling roll decreases as therotational velocity increases, as in the case of the single roll method.In the experiments, an average thickness of about 190 μm was measuredwith the rotation frequency of 500 rpm, and the average thickness was100-120 μm when the rotation frequency was 800 rpm.

However, mean thickness of the flakes produced by the second coolingroll is greater than that by the first cooling roll when the first andsecond cooling rolls had the same velocity. In the experiments, theaverage thickness was substantially constant at about 240 μm whether therotation frequency was 500 rpm or 800 rpm.

This is because flakes produced by the second cooling roll are made fromthe molten metal which has a higher velocity than that on the firstcooling roll, which will decrease a relative rotational velocity(peripheral velocity) of the second cooling roll, resulting incorrespondingly thicker flakes.

Thus, the average thickness of the flakes produced by the second coolingroll may be decreased by increasing the rotation frequency of only thesecond cooling roll. For example, the experiments revealed that flakeswith substantially identical thickness can be obtained by setting therotation frequencies of the first and second cooling rolls to be 800 rpmand 1150 rpm, respectively.

It is assumed that such decrease in the average flake thickness on thesecond cooling roll is determined by a peripheral velocity on its rollsurface. Accordingly, as in the case of differentiating the rotationalvelocities of the first and second cooling rolls 41 and 42 with the samediameter, the reduction in the average flake thickness can be alsoachieved by differentiating the roll diameters when the first and thesecond cooling rolls 41 and 43 have the same rotational frequency.

Accordingly, when the two cooling rolls 41 and 42 are used in themetal-flake manufacturing apparatus 40, the rotational velocity v1 ofthe first cooling roll 41 is differentiated from that v2 of the secondcooling roll 42 when the rolls have the same diameter as shown in FIG.5. Alternatively, the diameter d1 of the first cooling roll 41 isdifferentiated from that d3 of the second cooling roll 43 when the tworolls are rotated at the same rotation frequency, so that the latter hasa different peripheral velocity v3 as shown in FIG. 6. By thusincreasing the peripheral velocity of the second cooling roll 42 or 43,the average flake thickness manufactured by the first cooling roll 41and that by the second cooling roll 42 or 43 may be brought intosubstantially the same value.

Regardless of the peripheral velocities, the flakes produced by any ofthe cooling rolls 41, 42 or 43 have identical property, though therespective average thicknesses may be different.

Those embodiments have the same particulars as those in the earlierdescribed embodiments except for the peripheral velocities of thecooling rolls, and can of course produce the same performance andadvantageous effects. The embodiments may be further combined with thearrangement where the rotational axes are not in parallel with eachother.

Further embodiments of the invention will be described with reference toFIGS. 8A, 8B and 9.

FIGS. 8A and 8B and 9 are sectional views of the nozzle portion and agraph plotting the nozzle diameter against the flake thickness in thefurther embodiments of the metal-flake manufacturing apparatus accordingto the invention.

As shown in FIG. 8A, the metal-flake manufacturing apparatus 50 has anozzle 51 with a nozzle opening 52 increased in size. FIG. 8B shows thenozzle 51 with a nozzle opening 52 further increased in size. In theearlier described embodiments, the nozzle 14, when circular, had adiameter of 3 mm or less and a sectional area of 7.1 mm²; however, here,used are the nozzle opening 52 with a diameter ranging from 1.0 to 10.0mm and a sectional area ranging from 0.78 to 78 mm², which are largerthan the diameter of 3 mm or less and the sectional area of 7.1 mm².

The increase in diameter of the nozzle opening 52 results only in anincrease in the average thickness of the produced metal flakes, and doesnot cause any problems in their property. They can be used as materialsas they are.

As the diameter of the nozzle opening 52 is increased, more molten metalflies to the second cooling roll 54 without being solidified on thefirst cooling roll 53. Consequently, such molten metal flies radially ina plane perpendicular to the axis of the first cooling roll 53.Accordingly, the amount of molten metal that accumulates during contactof the solidified metal flakes to the surface of the second cooling roll54 increases, thereby producing thicker flakes.

The experiments using aluminum alloys revealed that the averagethickness of the flakes (metal flakes) increases as the sectional area(diameter) of the nozzle opening is increased as shown in FIG. 9.

The nozzle opening diameter may be in the range from 6 to 10 mm and itssectional area from 28 to 78 mm², which values are unusually largecompared with those used in the conventional manufacture of the metalflakes. Still, there can be obtained metal flakes in a highly efficientmanner.

The resultant metal flakes have no problems in their property and can beused as materials as they are.

Thus, the metal-flake manufacturing apparatus 50 may mass-producethicker metal flakes efficiently by increasing the size of the nozzleopening 52 of the nozzle 51.

The nozzle opening is not limited to circular in shape and may be shapedotherwise.

Thus, the metal-flake manufacturing apparatus according to the inventioncan manufacture metal flakes in a stable manner even when there is alarge amount of molten metal ejected.

Since the thin strip can be crushed halfway during the process ofmanufacture, no separate crusher is required and the storage box can beof smaller size.

Moreover, the direction of collection of the metal flakes may be freelyvaried by varying the arrangement or number of the cooling rolls.

The damage to and the rotative drive power required for the coolingrolls can be reduced as compared with the conventional double rollmethod.

The metal flakes can be stably produced even if operational conditionssuch as shape of the nozzle may be varied in an extensive range, whichis suitable for mass-production of metal flakes of constant quality.

As concretely described above with reference to the embodiments,according to the metal-flake manufacturing apparatus of the invention, aplurality of cooling rolls are spaced to have a gap of a size greaterthan thickness of metal thin bodies to be produced. A nozzle is providedto eject molten metal onto a surface of such cooling roll. The firstcooling roll quenches the molten metal from the nozzle into metal thinbodies. On the next cooling roll, the produced metal thin bodies are hitinto flakes while the excess molten metal is made into metal thinbodies. Thus, freedom in supply of molten metal is enhanced and metalflakes can be stably and efficiently produced.

The cooling rolls are arranged at different heights so that the producedmetal thin bodies are sequentially hit on the rolls, which increaseschances of the produced metal thin bodies being hit on the cooling rollsand contributes to obtaining further finer flakes and changeability ofthe flake withdrawal direction.

Rotational axes of the cooling rolls may be out of parallelism so that aflying direction of the metal thin bodies, which is on a planeperpendicular to the rotational axis, may be changed with increasedfreedom.

Moreover, the cooling rolls may be arranged to rotate at differentperipheral velocities. Differentiation in peripheral velocity betweenthe cooling rolls will contribute to controlling the thickness of themetal thin bodies produced; if the cooling rolls with the same diameterwere driven to rotate at the same peripheral velocity, thinner andthicker metal flakes would be produced on the upstream and downstreamrolls, respectively.

In addition, the cooling rolls may have different diameters so as tohave different peripheral velocities, which will contribute, just likethe above, to controlling the thickness of the metal thin bodies.

The nozzle may have a plurality of nozzle openings along the axis of thecooling roll. Provision of the nozzle openings in the shape of, forexample, slot or circle, along the axis of the roll will contribute tofurther effective production of metal flakes.

The respective nozzle openings may have a sectional area of 0.78-78 mm².Even with the nozzle-openings having the sectional area as large as of28-78 mm², which are unusually large as compared with those in theconventional production of metal flakes, thick metal flakes can beproduced with higher efficiency.

The nozzle and the cooling rolls may be placed in atmospheric gas andwindbreak members may be arranged to prevent the atmospheric gas frombeing swirled by the rotating cooling rolls. Manufacturing in theatmosphere such as inert gas will enhance the quality of the metalflakes produced. Prevention of the atmospheric gas from being swirled bythe rotating cooling rolls will prevent the nozzle from being cooled andprevent the metal flakes from being scattered.

Furthermore, gas from atmospheric gas supply nozzles may be directed toguide the metal flakes towards a storage box in which metal flakes areto be stored, which will prevent the metal flakes from being scatteredand contribute to efficient collection of the metal flakes in the box.

The storage box may have a cooler for cooling the collected metalflakes, which will contribute to further improvement of the metal flakecooling efficiency.

INDUSTRIAL APPLICABILITY

The present invention provides a metal-flake manufacturing apparatus formanufacturing, in a simple and efficient manner, quenched metal-flakematerials required for manufacture of thermoelectric materials, magnetmaterials, hydrogen storage alloys or the like.

What is claimed is:
 1. A metal-flake manufacturing apparatus comprising,a first cooling roll, a nozzle is arranged to eject molten metal on asurface of the first cooling roll not tangentially but in a direction ofcollision with the latter, said first cooling roll adapted to quench themolten metal from the nozzle through collision into metal thin bodiesand fly the produced metal thin bodies, and at least a second coolingroll on which the produced flown metal thin bodies are hit into flakes,said second cooling roll also serving for solidification of the moltenmetal not solidified by the first cooling roll, said cooling rolls beingspaced apart by a gap of a size greater than thickness of metal thinbodies.
 2. A metal-flake manufacturing apparatus according to claim 1,wherein said plurality of cooling rolls are arranged at differentheights so that the produced metal thin bodies are sequentially hit onthe rolls.
 3. A metal-flake manufacturing apparatus according to claim1, wherein rotational axes of said cooling rolls are mutually out ofparallelism.
 4. A metal-flake manufacturing apparatus according to claim1, wherein said cooling rolls are adapted to have different rolldiameters.
 5. A metal-flake manufacturing apparatus according to claim1, wherein said nozzle has a plurality of nozzle openings along an axisof the cooling roll.
 6. A metal-flake manufacturing apparatus accordingto claim 5, wherein the nozzle openings of said nozzle have a sectionalarea of 0.78-78 mm².
 7. A metal-flake manufacturing apparatus accordingto claim 1, wherein said nozzle and said cooling rolls are placed inatmospheric gas and windbreak members are arranged to prevent theatmospheric gas from being swirled by the rotating cooling rolls.
 8. Ametal-flake manufacturing apparatus according to claim 7, wherein gasfrom atmospheric gas supply nozzles for supplying said atmospheric gasis directed to guide the metal flakes toward a storage box in whichmetal flakes are to be stored.
 9. A metal-flake manufacturing apparatusaccording to claim 8, wherein said storage box has a cooler for coolingthe metal flakes stored.
 10. A metal-flake manufacturing apparatuscomprising, a first cooling roll, a nozzle is arranged to eject moltenmetal on a surface of the first cooling roll not tangentially but in adirection of collision with the latter, said first cooling roll adaptedto quench the molten metal from the nozzle into metal thin bodies and atleast a second cooling roll on which the produced metal thin bodies arehit into flakes, said second cooling roll also serving forsolidification of the molten metal not solidified by the first coolingroll, said cooling rolls being spaced apart by a gap of a size greaterthan thickness of metal thin bodies, and a crushing member configured tocrush the metal flakes, wherein said nozzle and said cooling rolls areplaced in atmospheric gas and windbreak members are arranged to preventthe atmospheric gas from being swirled by the rotating cooling rolls.11. A metal-flake manufacturing apparatus according to claim 10, whereingas from atmospheric gas supply nozzles for supplying said atmosphericgas directed to guide the metal flakes toward a storage box in whichmetal flakes are to be stored.
 12. A metal-flake manufacturing apparatusaccording to claim 11, wherein said storage box has a cooler for coolingthe metal flakes stored.